A conventional track shoe coupling for use in tracked construction machinery is illustrated in FIG. 5, wherein an inner link 1 and an outer link 2 are coupled together for relative rotation of one link with respect to the other link in the coupling. Specifically, the links 1 and 2 are articulation-coupled by a pivot pin 6 and an annular bushing 4. The generally cylindrical pivot pin 6 has an end part forcibly fitted into and immovably fixed in a generally cylindrical hole 5 of the outer link 2, while the annular bushing 4 is forcibly fitted into and immovably fixed in a generally cylindrical hole 3 of the inner link 1. The pin 6 extends freely through the axial opening 7 of the annular bushing 4 so that the bushing 4 and the pin 6 are slidably rotated with respect to each other upon relative rotation between links 1 and 2.
An annular counterbore 9, comprising a generally axial side wall surface 9a and a generally radial end wall surface 9b, is provided in the inside face of the outer link 2 at the periphery of hole 5. The counterbore 9 is open to the cylindrical surface of hole 5 as well as to the inside face of outer link 2. An annular thrust bearing 10 is positioned in the counterbore 9. An end face sealing assembly device S is also mounted in the counterbore 9 to prevent intrusion of foreign matter such as sand or muddy water onto the sliding surfaces of the bushing 4 and the pivot pin 6, and to prevent leakage of lubrication oil supplied to the annular gap between pivot pin 6 and bushing 4 from an oil hole 8 provided in the pivot pin 6.
There have been many proposals with respect to the end face sealing assembly device S, and FIG. 6 shows an end face sealing assembly device S.sub.1 which the present applicant proposed in Japanese Utility Model Laid-open (U) 2-36657. The end face sealing assembly device S.sub.1 is provided with an annular seal ring 12 having an approximately parallelogrammatic cross section in a radial plane, such as the plane of FIG. 6, with the seal ring 12 being made of a urethane-based rubber material. The seal ring 12 makes contact with and is supported by an annular support ring 11 made of a metallic material. The support ring 11 has a radial direction annular member 11a and an axial direction annular member 11b forming an approximately L-shaped cross section in a radial plane. The seal ring 12 has an annular lip part 12a which comes in contact with the end face 4a of the bushing 4 to form an annular seal. In addition, the end face sealing assembly device S.sub.1 is provided with a rubber load ring 13 which has an annular body member 13a with an approximately circular cross section in a radial plane, which applies a back pressure to an outer sloping surface 12b of the seal ring 12. The outer sloping surface 12b is a generally frustoconical annular surface which is inclined away from the bushing end face 4a and toward the longitudinal axis of the pin 6. Load ring 13 also has an annular projection 13b which extends outwardly and rearwardly from the body member 13a into contact with the axial surface 9a of the counterbore 9.
The set position P of the bushing 4, which is illustrated in FIG. 6 with a solid line for bushing end face 4a, shows a state where the bushing end face 4a is in sealing contact with lip 12a and is in contact with the thrust bearing 10 to press the thrust bearing 10 against the radial end wall 9b of the counterbore 9 so that the load ring 13 is compressed to a maximum amount. The free position Q of the bushing 4, which is illustrated with a broken line for bushing end face 4a in FIG. 6, shows a state where the bushing end face 4a is just free of contact with the seal ring 12 and is separated axially from the thrust bearing 10 by a stroke distance L. The service life of the seal depends on the length of an effective stroke L.sub.1, which is the distance from the set position P towards the free position Q during which the seal is effectively maintained.
However, this end face sealing assembly device S.sub.1 is constructed so that the annular circular body 13a of the load ring 13 is supported by the annular projection part 13b which is in contact with the axial wall surface 9a of the counterbore 9. Therefore, as the assembly device S.sub.1 approaches the free condition Q, the body member 13a is unwound from compressive contact with the projection part 13b while turning and extending forwardly in the axial direction toward the bushing end face 4a. Consequently, the conventional end face sealing assembly device S.sub.1 includes a problem that, when the assembly device approaches the free position Q, as shown with the curve A in FIG. 4, the seal line pressure suddenly falls if the amount of deflection exceeds the effective stroke L.sub.1. As the effective stroke L.sub.1 corresponding to the oil leakage limit line pressure is short, the follow-up property deteriorates.
Also, the load ring 13 of the end face sealing assembly device S.sub.1 is mounted on the external peripheral slope 12b of the seal ring 12, and therefore the load ring 13 can slip on the inclined surface 12b when in the set position P, with the result that the sealing surface pressure is not stabilized.